1. Field of the Invention
This relates to clamps generally, and more specifically to adjustable C-clamps.
2. Prior Art
It is well-known to have clamps generally in the form of a xe2x80x9cCxe2x80x9d formed by two arms depending from a back. Typically, a threaded rod passes through a matching threaded hole in the first arm and extends toward the second arm in such manner as an object can be secured between the second arm and the threaded rod.
A C-clamp is useful for securing objects of various sizes that fit between the threaded rod contact end and the second arm. Objects suitable for clamping by a given size C-clamp can range in size between a maximum when the threaded rod is effectively withdrawn away from the second arm and a minimum comparable to when the threaded rod is threaded through the hole toward the second arm essentially the full length of the threaded rod. For an object outside of this range, a C-clamp of a different size must be used. Commonly, a tool shop will have a wide range of C-clamps to accommodate objects of different sizes. Usually one will choose a C-clamp comparable in size to the object being clamped.
The primary object of the present invention is to have a C-clamp that is adjustable in effective width, extending the size range of objects that a single C-clamp can secure.
This object is achieved in a typical C-clamp modified to include a two-member back with one member extending from the other to a selective position where it is releasably secured. In the preferred embodiment, a first member telescopes from a channel in a second member. Across the channel at its entry end is a pin. The channel web recedes from its entry end to provide a slot through which the first member enters under the pin. The pin blocks the channel at its top, so the first member enters the channel at an angle to the channel web and then rotates down onto the web and into engagement with the pin.
When the first member is rotated into contact with the channel web, the pin engages one of a plurality of grooves in the top of the first member to prevent the first member from moving in the channel. To later adjust the relative position of the first member in the channel, it is rotated away from the web and the pin. After the first member is repositioned, it is rotated back into contact with the web and the pin is received into a different one of the plurality of slots.
Significantly, when an object is clamped in the clamp, the object is forcibly pressed against an arm depending from the first member, which causes a rotational force on the first member. That is, the first member is urged up against the pin further locking the pin in the selective first member groove. The pin also becomes a fulcrum in a lever action that urges the first member portion in the channel hard against the channel web in a lever action causing increased frictional resistance to the first member sliding in the channel as well as maintaining the pin in the groove.
In an alternative embodiment, the pin moves in the second member out of engagement with the first member rather than the first member moving out of engagement with a stationary pin. In such case, the second member is typically a tube and the first member simply telescopes in and out of the tube. Typically, the pin passes through a transverse hole in the tube and into a selective one of a plurality of transverse holes in the first member aligned to receive the pin. The pin should be deemed only representative of many mechanisms known in the art that could releasably secure the back members together during use. Other configurations, such as a ratchet or a pawl in the second member engaging a rack on the first member are deemed equivalent to the pin.